ABSTRACT
The level of phosphorus must be carefully monitored for proper and effective utilization of coal and coal ash. The phosphorus content needs to be assessed to optimize combustion efficiency and maintenance costs of power plants, ensure quality, and minimize the environmental impact of coal and coal ash. The detection of low levels of phosphorus in coal and coal ash is a significant challenge due to its complex chemical composition and low concentration levels. Effective monitoring requires accurate and sensitive equipment for the detection of phosphorus in coal and coal ash. X-ray fluorescence (XRF) is a commonly used analytical technique for the determination of phosphorus content in coal and coal ash samples but proves challenging due to their comparatively weak fluorescence intensity. Fourier Transform Infrared spectroscopy (FTIR) emerges as a promising alternative that is simple, rapid, and cost-effective. However, research in this area has been limited. Until now, only a limited number of research studies have outlined the estimation of major elements in coal, predominantly relying on FTIR spectroscopy. In this article, we explore the potential of FTIR spectroscopy combined with machine learning models (piecewise linear regression-PLR, partial least square regression-PLSR, random forest-RF, and support vector regression-SVR) for quantifying the phosphorus content in coal and coal ash. For model development, the methodology employs the mid-infrared absorption peak intensity levels of phosphorus-specific functional groups and anionic groups of phosphate minerals at various working concentration ranges of coal and coal ash. This paper proposes a multi-model estimation (using PLR, PLSR, and RF) approach based on FTIR spectral data to detect and rapidly estimate low levels of phosphorus in coal and its ash (R 2 of 0.836, RMSE of 0.735 ppm, RMSE (%) of 34.801, MBE of - 0.077 ppm, MBE (%) of 5.499, and MAE of 0.528 ppm in coal samples and R 2 of 0.803, RMSE of 0.676 ppm, RMSE (%) of 38.050, MBE of - 0.118 ppm, MBE (%) of 4.501, and MAE of 0.474 ppm in coal ash samples). Our findings suggest that FTIR combined with the multi-model approach combining PLR, PLSR, and RF regression models is a reliable tool for rapid and near-real-time measurement of phosphorus in coal and coal ash and can be suitably modified to model phosphorus content in other natural samples such as soil, shale, etc.
ABSTRACT
The Barakar coal seams of Jharia Basin have been evaluated for the geochemical and petrographic control of coalbed methane (CBM) reservoir characteristics. The coal core samples are analyzed for the total gas content, gas chromatography, stable isotopes (δ13C1), and geochemical, petrographic and vitrinite reflectance. The significant face (1.6-7.6%) and butt (0.9-5.3%) cleat intensities specify the brittle characteristics of coal seams and also favor the gas flow mechanism. The thermal cracking position of hydrocarbon compounds was evaluated, which signifies the excellent source rock potential of coal for gas genesis. The inputs of type III and IV organic matter illustrated by the van Krevelan diagram signify thermally matured coal seams. The low values of sorption time (τ) between 2.1 and 5.6 days designate excellent diffusion characteristics that is favored by the cleat intensities. The values of total gas content and sorption capacity (V L) reveal that moderate saturation indicates a higher gas content, attributed to the seam thickness and thermal maturity. Similarly, the CH4 concentrations (89.4-96.6 vol %) display that the genesis pattern is a function of thermal maturity; however, some samples fall under the mixed type substantiated by the stable isotope (δ13C1) (-25.40 to -64.90), emphasizing bacterial hold by seasonal influx of freshwater. The ternary facies diagram (Vmmf, Immf, Lmmf) also supports notable generation of methane gas and storage in the coal seams of the Jharia Basin. The volume percentage of each maceral determined from petrographic study was used to estimate the fraction of conversion (f) of the organic content (0.19-0.97). The values of "f" indicate that the Barakar coal has undergone maximum conversion, which may be attributed to the older early Permian coal and placed at a greater depth after deposition due to the basin sink. The high fraction of conversion and thermal maturity may also be explained due to the existence of volcanic intrusion (sills and dykes). The uniformity in the distribution of functional groups is shown by Fourier transform infrared spectra representing moderate to stronger peaks of aromatic carbon (CO and C=C) between 1750 and 1450 cm-1, which indicates that the presence of a larger total organic carbon content likely validates the removal of aliphatic compounds during gas genesis. The variations in the BET curve have been categorized as H1 hysteresis following the type II adsorption pattern, suggesting that cylindrical pores and some of the coal samples have a type IV H4 hysteresis pattern, characterized as the slit type of pores. The average values of the pore diameter indicate the dominance of mesopores suitable for gas storage and release and hence a major part of the pore volume is contributed by the mesopores having a width mainly between 2.98 and 4.48 nm. The significant role of the meso-macropore network (D 1 fractals) in methane storage of the coal matrix is represented by a moderate positive relationship of V L with D 1, which accentuated that meso-macropores developed due to devolatilization and dehydration of organic matter and also by geochemical alteration of macerals and minerals formed heterogenetic inner surfaces suitable for gas adsorption. The estimated recoverable resource applying Mavor Pratt methods is 8.78 BCM, which is found to be a more realistic resource value for the studied CBM block.
ABSTRACT
The carbon-rich Barakar and Barren Measures shale beds of the Jharia basin were evaluated for variation in pore size, pore structure, and fractal dimensions. The shale core samples were obtained from exploratory boreholes drilled at the Jharia basin. The shale samples were analyzed for organo-inorganic composition by FTIR, pore size, and pore structure using BET low-pressure N2 adsorption and pore geometry through FE-SEM photographs. The shale samples have significant carbon-rich content and are intercalated-banded in nature. The pore structures were evaluated through N2 isotherms and validated by SEM images, revealing the mixed contribution of organo-inorganic matter in pore formations controlled by geochemical alteration, diagenesis, and mineral interaction. The rough internal surfaces of the pore were evaluated by categorizing them into fractals D 1, D 2, and D 3. It is observed that the D 2 type of fractals is in abundance associated with mesopores. The positive trend of fractals with pore size, pore structure, depth, fixed carbon, and TOC suggests the influence of different parameters on the formation of pore internal rugged surfaces in shale beds. The FE-SEM images indicate shallow to deep pores with different pore structures with fair to good pore connectivity. In summary, the shale beds of Jharia have heterogeneous complex pore structures, a rough surface, and sorption mechanisms controlled by weathering/alteration, depositional conditions, and organo-inorganic content. In shale beds, gas storage and transport phenomena are directly related to pore size distribution, pore structure, and associated fractal dimensions. The calculated values using the proposed empirical models for porosity (EPOf) and permeability (EPEf) showed excellent linear correlation with the measured porosity (MPOc, R 2 = 0.8577) and permeability (MPEc, R 2 = 0.8577), which are close to measured values. The curve matching of EPOf with MPOc and EPEf with MPEc follows a similar path, validating the results and suitability of the models. Hence, the proposed models may be considered to estimate the porosity and permeability of shale and coal beds.
ABSTRACT
The organo-lithotype properties of Barakar and Raniganj Formation coal seams have been investigated to assess the process of cleat origin, occurrence, and their influence on strength properties. Coal cleats have wide applications in coalbed methane gas recovery, underground mine strata mechanics, beneficiation, and pulverization. However, there is very limited information available on the cleat occurrence and controlling parameters of Indian coals. In this view, a total of 31 coal samples were retrieved from eight exploratory boreholes intersecting coal-bearing formations like Barakar and Raniganj in the Raniganj Coalfield. We identified four distinct lithotypes in coal seams: (i) B, bright coal; (ii) Db, dull banded coal; (iii) Bb, bright banded coal; and (iv) Bd, banded coal. The abundance of bright-band-associated lithotype indicates organic matter that attained the early anoxic conditions after deposition. The cleat system in Barakar coal is comparatively better than in Raniganj coal controlled by the lithotype, type of organic matter, thermal maturity, and gelification extent. The carbon enrichment process in coal mainly controls the megascopic cleat genesis pattern. The positive trend of cleat intensities with the depth of coal seams as determined by megascopic, microscopic, and scanning electron microscope (SEM) studies postulates that the macro- to nanocleats are interdependent and developed during devolatilization due to loss of plasticity. The field emission scanning electron microscopy (FE-SEM) photographs have shown intricate microfractures and pore structures owing to the epigenetic characteristics. Vitrinite bands indicate that it comprises the partially deformed planer cleat system. The resistance to quartz weathering nature attributed to coal brittleness properties also contributed to cleat genesis. The total clay content exhibits an inverse relationship with different cleat intensities, suggesting that hydrous clay swells due to its inherent ultrafine characteristics, thus not supporting the cleat construction. However, it ropes the development of the irregular crack when organo-inorganic matter achieves the dry thermal conditions. The microfractures linked with different pore structures in studied coals can be classified into seven types: (i) vitrite-associated regular open-slit pores, (ii) vitriinertite-char allied irregular pores, (iii) irregular fracture-pore partially filled with clay, (iv) fissile pores along bedding planes of clay, (v) organic pores evolved due to external heat received from intrusives, (vi) deep organic pores evolved during compaction and thermal transformation, and (vii) pore fractures blocked by boghead algae. The clay content showed a positive relationship with physicomechanical properties, signifying the cementing characteristics of clay holding fractures and pores. There is significant variation in the strength properties of Barakar and Marren measures coal influenced by thermal maturity, lithotype characteristics, and organo-inorganic content.
